C6

Question 1

What is a cathode ?

Answer 1

Negative electrode

Question 2

What is an anode ?

Answer 2

Positive electrode

Question 3

A solution of copper sulfate is being electrolysed.
What elements would be discharged at each electrode ?

Answer 3

anode: oxygen (OH-)
cathode: copper (Cu2+)

Question 4

What is the order of discharge at the anode ?

Answer 4

halogens > hydroxides > all other negative ions

Question 5

Write the half equation for the discharge of copper at a cathode.

Answer 5

Cu2+ + 2e- –> Cu

Question 6

Write the half equation for the discharge of chlorine at the anode.

Answer 6

Cl- –> Cl + e-

Question 7

What does ‘OIL RIG’ stand for ?

Answer 7

Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons)

Question 8

If chlorine is discharged at the anode, has it been reduced or oxidised ?

Answer 8

oxidised (loses one electron)

Question 9

If copper (II) is discharged at the cathode, has it been reduced or oxidised ?

Answer 9

reduced (gains 2 electrons)

Question 10

What ore do you get aluminium oxide (Al2O3) from ?

Answer 10

Bauxite

Question 11

How is aluminium extracted via electrolysis ?

Answer 11

• aluminium oxide extracted from bauxite
• aluminium oxide heated with molten cryolite to reduce energy costs (can be electrolysed at 850’C instead of 1500’C)
• at anode, aluminium discharged
• at cathode, oxygen gas discharged
• oxygen reacts with hot carbon electrodes to give carbon dioxide, which eventually destroys the electrodes
• electrodes are regularly replaced

Question 12

What is brine ?

Answer 12

conc. sodium chloride solution

Question 13

Give the products of the electrolysis of brine.

Answer 13

• sodium hydroxide solution
• chlorine gas (discharged at anode)
• hydrogen gas (discharged at cathode)

Question 14

If either hydrogen or another positive ion may be discharged as its element at the cathode, which will be discharged ?

Answer 14

Hydrogen (gas)